Genomic profiling for clinical decision making in lymphoid neoplasms.

With the introduction of large-scale molecular profiling methods and high-throughput sequencing technologies, the genomic features of most lymphoid neoplasms have been characterized at an unprecedented scale. Although the principles for the classification and diagnosis of these disorders, founded on a multidimensional definition of disease entities, have been consolidated over the past 25 years, novel genomic data have markedly enhanced our understanding of lymphomagenesis and enriched the description of disease entities at the molecular level. Yet, the current diagnosis of lymphoid tumors is largely based on morphological assessment and immunophenotyping, with only few entities being defined by genomic criteria. This paper, which accompanies the International Consensus Classification of mature lymphoid neoplasms, will address how established assays and newly developed technologies for molecular testing already complement clinical diagnoses and provide a novel lens on disease classification. More specifically, their contributions to diagnosis refinement, risk stratification, and therapy prediction will be considered for the main categories of lymphoid neoplasms. The potential of whole-genome sequencing, circulating tumor DNA analyses, single-cell analyses, and epigenetic profiling will be discussed because these will likely become important future tools for implementing precision medicine approaches in clinical decision making for patients with lymphoid malignancies.

Entities versus diseases: Myers et al. propose distinct aspects of adult T-cell lymphoma/leukemia.

Not available.

A targeted gene signature stratifying mediastinal gray zone lymphoma into classical HL-like or PMBL-like subtypes.

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Outcomes and prognostic factors in angioimmunoblastic T-cell lymphoma: final report from the international T-cell Project.

Angioimmunoblastic T-cell lymphoma (AITL) is a unique subtype of peripheral T-cell lymphoma (PTCL) with distinct clinicopathologic features and poor prognosis. We performed a subset analysis of 282 patients with AITL enrolled between 2006 and 2018 in the international prospective T-cell Project (NCT01142674). The primary and secondary end points were 5-year overall survival (OS) and progression-free survival (PFS), respectively. We analyzed the prognostic impact of clinical covariates and progression of disease within 24 months (POD24) and developed a novel prognostic score. The median age was 64 years, and 90% of patients had advanced-stage disease. Eighty-one percent received anthracycline-based regimens, and 13% underwent consolidative autologous stem cell transplant (ASCT) in first complete remission (CR1). Five-year OS and PFS estimates were 44% and 32%, respectively, with improved outcomes for patients who underwent ASCT in CR1. In multivariate analysis, age ≥60 years, Eastern Cooperative Oncology Group performance status >2, elevated C-reactive protein, and elevated ß2 microglobulin were associated with inferior outcomes. A novel prognostic score (AITL score) combining these factors defined low-, intermediate-, and high-risk subgroups with 5-year OS estimates of 63%, 54%, and 21%, respectively, with greater discriminant power than established prognostic indices. Finally, POD24 was a powerful prognostic factor with 5-year OS of 63% for patients without POD24 compared with only 6% for patients with POD24 (P < .0001). These data will require validation in a prospective cohort of homogeneously treated patients. Optimal treatment of AITL continues to be an unmet need, and novel therapeutic approaches are required.

A Rare Case of BIA-ALCL Mass Associated with Mastectomy Skin Flap Erythema After Immunization with COVID-19.

BACKGROUND: The immune response to breast implants after COVID-19 disease or COVID-19 vaccine administration includes acute inflammatory manifestations, capsular contracture and seroma. Breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) is a very rare tumor in which numerous up-regulated pro-inflammatory immunological pathways activate a T cell lymphoproliferative disorder. METHODS: The first reported case of a BIA-ALCL hidden mass clinically manifesting with inflammatory signs after SARS-CoV-2 infection and vaccinations is here described. RESULTS: Complete capsulectomy and adjuvant chemotherapy were performed and immediately after the surgical procedure local inflammatory signs disappeared; no evidence of disease was present 1 year later. CONCLUSIONS: Immunological stimulation by COVID-19 disease and vaccines may highlight some rare clinical manifestations of BIA-ALCL; persistent inflammatory symptomatology over breast implants should be investigated using second-level imaging. LEVEL OF EVIDENCE V: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Prognostic impact of TP53 mutation in newly diagnosed diffuse large B-cell lymphoma patients treated in the FIL-DLCL04 trial.

The prognostic role of TP53 disruption has been established in diffuse large B-cell lymphoma (DLBCL). Aim of this analysis was to correlate TP53 mutations by Sanger sequencing, cell of origin (COO) profile by Lymph2Cx panel on the NanoString platform and MYC, BCL2 and BCL6 overexpression or re-arrangements by immunohistochemistry (IHC) and fluorescent in-situ hybridization (FISH), with outcome in DLBCL patients enrolled into the FIL-DLCL04 trial (NCT00499018). One hundred and twenty-five DLBCL patients with tumour block available were analyzed. TP53 was mutated in 11/125 (9%) cases; 60/125 patients received high-dose chemoimmunotherapy up-front, as for the randomization arm; COO was reported in 88 patients: 48 germinal centre B-cell like, 25 activated B-cell like and 17 unclassified; 26 patients were double expressors in IHC and 11 double hit in FISH. After a median follow-up of 72 months, five-year failure-free survival (FFS) for TP53 mutated versus wild-type was 24% and 72%, and five-year overall survival (OS) was 34% and 83%, respectively. Adjusted hazard ratio (HR) was 2·28 [95% confidence interval (CI) 0·89-5·86, p = 0·086] and 4·05 (95% CI 1·37-11·97, p = 0·011) for FFS and OS, respectively. In this series of young DLBCL patients, TP53 gene mutation identified a poor prognosis subgroup, regardless of treatment and other biological markers.

Characteristics and clinical outcomes of patients with ALK-positive anaplastic large cell lymphoma: Report from the prospective international T-cell lymphoma project.

The T-cell Lymphoma Project is an international registry prospective study that enrolled patients with newly diagnosed peripheral T-cell and NK-cell lymphomas (PTCL). The main objective was to define the clinical features and outcomes, establishing a robust benchmark for future clinical trials. Seventy-four institutions from 14 countries in North America, South America, Europe, and Asia collected data on patients diagnosed and treated at their respective centers between September 2006 and February 2018. Among 1553 PTCL patients, 131 (8.4% of the total cohort) were confirmed to have anaplastic large cell lymphoma - kinase positive (ALCL, ALK+). The median age of the patients was 39 years (18-84). Sixty-five patients (66%) had advanced-stage disease, although majority (45 patients, 54%) had a low-risk International Prognostic Index (IPI) score (0-1). Of 97 patients treated with chemotherapy, 97% received anthracycline-containing regimens. The overall response rate was 81%, with 69 patients (70%) achieving complete remission. Estimated OS and PFS at 3 years were 77% (95% CI: 54%-99%) and 68% (95% CI: 46%-90%), respectively, and at 5 years were very similar, 77% of OS (95% CI: 62%-92%) and 64% of PFS (95% CI: 34%-94%). Multivariate analysis for PFS showed advanced stage (hazard ratios [HR]: 4.72, 95% CI: 1.43-23.9, p = 0.015), elevated lactate dehidrogenade (LDH) (HR 4.85; 95% CI: 1.73-13.60, p = 0.001), and Eastern Cooperative Oncology Group Performance Status scale (ECOG-PS) ≥2 (HR: 5.25; 95% CI: 1.68-16.4, p = 0.024). For OS, elevated LDH (HR: 3.77; 95% CI: 1.98-14.17, p = 0.014) and ECOG-PS ≥2 (HR: 4.59; 95% CI: 1.46-14.39, p = 0.004) were identified. In summary, although the outcome of ALK+ ALCL is superior to that of other PTCLs, it remains sufficiently favorable, given the young median age of the patients. Our results confirm the usefulness of both IPI and Prognostic Index for T-cell Lymphoma (PIT) in identifying groups of patients with different outcomes. Clinical Trials ID: NCT01142674.

NR1H3 (LXRα) is associated with pro-inflammatory macrophages, predicts survival and suggests potential therapeutic rationales in diffuse large b-cell lymphoma.

The role of macrophages (Mo) and their prognostic impact in diffuse large B-cell lymphomas (DLBCL) remain controversial. By regulating the lipid metabolism, Liver-X-Receptors (LXRs) control Mo polarization/inflammatory response, and their pharmacological modulation is under clinical investigation to treat human cancers, including lymphomas. Herein, we surveyed the role of LXRs in DLBCL for prognostic purposes. Comparing bulk tumors with purified malignant and normal B-cells, we found an intriguing association of NR1H3, encoding for the LXR-α isoform, with the tumor microenvironment (TME). CIBERSORTx-based purification on large DLBCL datasets revealed a high expression of the receptor transcript in M1-like pro-inflammatory Mo. By determining an expression cut-off of NR1H3, we used digital measurement to validate its prognostic capacity on two large independent on-trial and real-world cohorts. Independently of classical prognosticators, NR1H3high patients displayed longer survival compared with NR1H3low cases and a high-resolution Mo GEP dissection suggested a remarkable transcriptional divergence between subgroups. Overall, our findings indicate NR1H3 as a Mo-related biomarker identifying patients at higher risk and prompt future preclinical studies investigating its mouldability for therapeutic purposes.

Whole exome sequencing reveals mutations in FAT1 tumor suppressor gene clinically impacting on peripheral T-cell lymphoma not otherwise specified.

Peripheral T-cell lymphoma not otherwise specified represents a diagnostic category comprising clinically, histologically, and molecularly heterogeneous neoplasms that are poorly understood. The genetic landscape of peripheral T-cell lymphoma not otherwise specified remains largely undefined, only a few sequencing studies having been conducted so far. In order to improve our understanding of the genetics of this neoplasm, we performed whole exome sequencing along with RNA-sequencing in a discovery set of 21 cases. According to whole exome sequencing results and mutations previously reported in other peripheral T-cell lymphomas, 137 genes were sequenced by a targeted deep approach in 71 tumor samples. In addition to epigenetic modifiers implicated in all subtypes of T-cell neoplasm (TET2, DNMT3A, KMT2D, KMT2C, SETD2), recurrent mutations of the FAT1 tumor suppressor gene were for the first time recorded in 39% of cases. Mutations of the tumor suppressor genes LATS1, STK3, ATM, TP53, and TP63 were also observed, although at a lower frequency. Patients with FAT1 mutations showed inferior overall survival compared to those with wild-type FAT1. Although peripheral T-cell lymphoma not otherwise specified remains a broad category also on molecular grounds, the present study highlights that FAT1 mutations occur in a significant proportion of cases, being provided with both pathogenetic and prognostic impact.

Correction: Whole exome sequencing reveals mutations in FAT1 tumor suppressor gene clinically impacting on peripheral T-cell lymphoma not otherwise specified.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Blastic plasmacytoid dendritic cell neoplasm: genomics mark epigenetic dysregulation as a primary therapeutic target.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic malignancy for which there is still no effective therapy. In order to identify genetic alterations useful for a new treatment design, we used whole-exome sequencing to analyze 14 BPDCN patients and the patient-derived CAL-1 cell line. The functional enrichment analysis of mutational data reported the epigenetic regulatory program to be the most significantly undermined (P<0.0001). In particular, twenty-five epigenetic modifiers were found mutated (e.g. ASXL1, TET2, SUZ12, ARID1A, PHF2, CHD8); ASXL1 was the most frequently affected (28.6% of cases). To evaluate the impact of the identified epigenetic mutations at the gene-expression and Histone H3 lysine 27 trimethylation/acetylation levels, we performed additional RNA and pathology tissue-chromatin immunoprecipitation sequencing experiments. The patients displayed enrichment in gene signatures regulated by methylation and modifiable by decitabine administration, shared common H3K27-acetylated regions, and had a set of cell-cycle genes aberrantly up-regulated and marked by promoter acetylation. Collectively, the integration of sequencing data showed the potential of a therapy based on epigenetic agents. Through the adoption of a preclinical BPDCN mouse model, established by CAL-1 cell line xenografting, we demonstrated the efficacy of the combination of the epigenetic drugs 5'-azacytidine and decitabine in controlling disease progression in vivo.

Prospective subgroup analyses of the randomized MCL-002 (SPRINT) study: lenalidomide versus investigator's choice in relapsed or refractory mantle cell lymphoma.

In the mantle cell lymphoma (MCL)-002 study, lenalidomide demonstrated significantly improved median progression-free survival (PFS) compared with investigator's choice (IC) in patients with relapsed/refractory MCL. Here we present the long-term follow-up data and results of preplanned subgroup exploratory analyses from MCL-002 to evaluate the potential impact of demographic factors, baseline clinical characteristics and prior therapies on PFS. In MCL-002, patients with relapsed/refractory MCL were randomized 2:1 to receive lenalidomide (25 mg/day orally on days 1-21; 28-day cycles) or single-agent IC therapy (rituximab, gemcitabine, fludarabine, chlorambucil or cytarabine). The intent-to-treat population comprised 254 patients (lenalidomide, n = 170; IC, n = 84). Subgroup analyses of PFS favoured lenalidomide over IC across most characteristics, including risk factors, such as high MCL International Prognostic Index score, age ≥65 years, high lactate dehydrogenase (LDH), stage III/IV disease, high tumour burden, and refractoriness to last prior therapy. By multivariate Cox regression analysis, factors associated with significantly longer PFS (other than lenalidomide treatment) included normal LDH levels (P < 0·001), nonbulky disease (P = 0·045), <3 prior antilymphoma treatments (P = 0·005), and ≥6 months since last prior treatment (P = 0·032). Overall, lenalidomide improved PFS versus single-agent IC therapy in patients with relapsed/refractory MCL, irrespective of many demographic factors, disease characteristics and prior treatment history.

Targeting Mutant BRAF in Relapsed or Refractory Hairy-Cell Leukemia.

BACKGROUND: BRAF V600E is the genetic lesion underlying hairy-cell leukemia. We assessed the safety and activity of the oral BRAF inhibitor vemurafenib in patients with hairy-cell leukemia that had relapsed after treatment with a purine analogue or who had disease that was refractory to purine analogues. METHODS: We conducted two phase 2, single-group, multicenter studies of vemurafenib (at a dose of 960 mg twice daily)--one in Italy and one in the United States. The therapy was administered for a median of 16 weeks in the Italian study and 18 weeks in the U.S. study. Primary end points were the complete response rate (in the Italian trial) and the overall response rate (in the U.S. trial). Enrollment was completed (28 patients) in the Italian trial in April 2013 and is still open (26 of 36 planned patients) in the U.S. trial. RESULTS: The overall response rates were 96% (25 of 26 patients who could be evaluated) after a median of 8 weeks in the Italian study and 100% (24 of 24) after a median of 12 weeks in the U.S. study. The rates of complete response were 35% (9 of 26 patients) and 42% (10 of 24) in the two trials, respectively. In the Italian trial, after a median follow-up of 23 months, the median relapse-free survival was 19 months among patients with a complete response and 6 months among those with a partial response; the median treatment-free survival was 25 months and 18 months, respectively. In the U.S. trial, at 1 year, the progression-free survival rate was 73% and the overall survival rate was 91%. Drug-related adverse events were usually of grade 1 or 2, and the events most frequently leading to dose reductions were rash and arthralgia or arthritis. Secondary cutaneous tumors (treated with simple excision) developed in 7 of 50 patients. The frequent persistence of phosphorylated ERK-positive leukemic cells in bone marrow at the end of treatment suggests bypass reactivation of MEK and ERK as a resistance mechanism. CONCLUSIONS: A short oral course of vemurafenib was highly effective in patients with relapsed or refractory hairy-cell leukemia. (Funded by the Associazione Italiana per la Ricerca sul Cancro and others; EudraCT number, 2011-005487-13; ClinicalTrials.gov number NCT01711632.).

The 2016 revision of the World Health Organization classification of lymphoid neoplasms.

A revision of the nearly 8-year-old World Health Organization classification of the lymphoid neoplasms and the accompanying monograph is being published. It reflects a consensus among hematopathologists, geneticists, and clinicians regarding both updates to current entities as well as the addition of a limited number of new provisional entities. The revision clarifies the diagnosis and management of lesions at the very early stages of lymphomagenesis, refines the diagnostic criteria for some entities, details the expanding genetic/molecular landscape of numerous lymphoid neoplasms and their clinical correlates, and refers to investigations leading to more targeted therapeutic strategies. The major changes are reviewed with an emphasis on the most important advances in our understanding that impact our diagnostic approach, clinical expectations, and therapeutic strategies for the lymphoid neoplasms.

Rituximab-dose-dense chemotherapy with or without high-dose chemotherapy plus autologous stem-cell transplantation in high-risk diffuse large B-cell lymphoma (DLCL04): final results of a multicentre, open-label, randomised, controlled, phase 3 study.

BACKGROUND: The prognosis of young patients with diffuse large B-cell lymphoma at high risk (age-adjusted International Prognostic Index [aa-IPI] score 2 or 3) treated with R-CHOP (rituximab, cyclophosphamide, vincristine, doxorubicin, and prednisone) is poor. The aim of this study was to investigate the possible benefit of intensification with high-dose chemotherapy and autologous stem-cell transplantation as part of first-line treatment in these patients. METHODS: We did a multicentre, open-label, randomised, controlled, phase 3 trial with a 2 × 2 factorial design to compare, at two different R-CHOP dose levels, a full course of rituximab-dose-dense chemotherapy (no transplantation group) versus an abbreviated course of rituximab-dose-dense chemotherapy followed by consolidation with R-MAD (rituximab plus high-dose cytarabine plus mitoxantrone plus dexamethasone) and high-dose BEAM chemotherapy (carmustine, etoposide, cytarabine, and melphalan) plus autologous stem-cell transplantation (transplantation group) in young patients (18-65 years) with untreated high-risk diffuse large B-cell lymphoma (aa-IPI score 2-3). At enrolment, patients were stratified according to aa-IPI score and randomly assigned (1:1:1:1) to receive R-CHOP (intravenous rituximab 375 mg/m2, cyclophosphamide 750 mg/m2, doxorubicin 50 mg/m2, and vincristine 1·4 mg/m2 on day 1, plus oral prednisone 100 mg on days 1-5) delivered in a 14-day cycle (R-CHOP-14) for eight cycles; high-dose R-CHOP-14 (R-MegaCHOP-14; R-CHOP-14 except for cyclophosphamide 1200 mg/m2 and doxorubicin 70 mg/m2) for six cycles; R-CHOP-14 for four cycles followed by R-MAD (intravenous rituximab 375 mg/m2 on day 1 or 4 plus intravenous cytarabine 2000 mg/m2 and dexamethasone 4 mg/m2 every 12 h on days 1-3 plus intravenous mitoxantrone 8 mg/m2 on days 1-3) plus BEAM (intravenous carmustine 300 mg/m2 on day -7, intravenous cytarabine 200 mg/m2 twice a day on days -6 to -3, intravenous etoposide 100 mg/m2 twice a day on days -6 to -3, plus intravenous melphalan 140 mg/m2 on day -2) and autologous stem-cell transplantation (day 0); or R-MegaCHOP-14 for four cycles followed by R-MAD plus BEAM and autologous stem-cell transplantation. The primary endpoint was failure-free survival at 2 years in the intention-to-treat population. This study is registered with EudraCT (2005-002181-14; 2007-000275-42) and with ClinicalTrials.gov, number NCT00499018. FINDINGS: Between Jan 10, 2006, and Sept 8, 2010, 399 patients were randomly assigned to receive transplantation (n=199) or no transplantation (n=200); 203 patients were assigned to receive R-CHOP-14 and 196 were assigned to receive R-MegaCHOP-14. With a median follow-up of 72 months (IQR 57-88), 2-year failure-free survival was 71% (95% CI 64-77) in the transplantation group versus 62% (95% CI 55-68) in the no transplantation group (hazard ratio [HR] 0·65 [95% CI 0·47-0·91]; stratified log-rank test p=0·012). No difference in 5-year overall survival was observed between these groups (78% [95% CI 71-83] versus 77% [71-83]; HR 0·98 [0·65-1·48]; stratified log-rank test p=0·91). Grade 3 or worse haematological adverse events were reported in 183 (92%) of 199 patients in the transplantation group versus 135 (68%) of 200 patients in the no transplantation group. Grade 3 or worse non-haematological adverse events were reported in 90 (45%) versus 31 (16%); the most common grade 3 or worse non-haematological adverse event was gastrointestinal (49 [25%] vs 19 [10%]). Treatment-related deaths occurred in 13 (3%) patients; eight in the transplantation group and five in the no transplantation group. INTERPRETATION: Abbreviated rituximab-dose-dense chemotherapy plus R-MAD plus BEAM and autologous stem-cell transplantation reduced the risk of treatment failure compared with full course rituximab-dose-dense chemotherapy in young patients with diffuse large B-cell lymphoma at high risk. However, these results might not be clinically meaningful, since this improvement did not reflect an improvement in overall survival. These results do not support further consideration of the use of intensification of R-CHOP as an upfront strategy in patients with diffuse large B-cell lymphoma with poor prognosis. FUNDING: Fondazione Italiana Linfomi.

Follicular helper T-cell-related lymphomas.

In this issue of Blood, Wang et al describe the occurrence and pathogenetic relevance of IDH2R172 mutations in angioimmunoblastic T-cell lymphoma (AITL).

Cytotoxic Epstein-Barr virus-positive large B cell lymphoma: a regulatory B cell-derived neoplasia?

AIMS: A new subtype of granzyme B (GrB)-producing regulatory B cells (Bregs ) has been described recently; these peculiar cytotoxic B cells are increased significantly in interleukin (IL)-21-rich settings, and in particular during HIV and Epstein-Barr virus (EBV) infection. Our aim is to report a unique case of an EBV-positive diffuse large B cell lymphoma (DLBCL) with cytotoxic features arisen in an HIV+ patient, and to understand if this lesion may represent a proliferation of neoplastic cytotoxic Bregs . METHODS AND RESULTS: We describe a 66-year-old male patient who presented with cervical lymph node enlargement and B symptoms; subsequently, HIV infection was diagnosed. Histopathological, immunohistochemical and molecular studies were performed, and revealed an EBV-positive DLBCL with cytotoxic features. Considering the immunological setting and unconventional phenotype observed, we tried to evaluate further the expression of GrB and IL-21 in another 150 aggressive B cell lymphomas (17 of 150 EBV+ , two of 150 EBV+ /HIV+ ). Minimal dot-like expression of GrB was found in seven lymphomas (in fewer than 1% of tumour cells), three of which were EBV-positive. CONCLUSIONS: Breg origin has never been reported in B cell lymphomas. We describe an exceptional case of EBV-positive DLBCL with aberrant expression of cytotoxic markers in a patient with a previously unknown HIV infection. We propose cytotoxic Bregs as a possible normal counterpart for this unusual tumour.

The emerging role of GSK-3ß in the pathobiology of classical Hodgkin lymphoma.

AIMS: Glycogen synthase kinase-3 beta (GSK-3ß) is a serine/threonine kinase involved in glycogen metabolism, cell cycle progression, differentiation, embryogenesis, migration, metabolism, survival and cellular senescence. Its main biological function is to inhibit ß-catenin by sequestration and promotion of its proteasomal degradation in the Wnt canonical pathway; however, GSK-3ß interacts with multiple signalling pathways, and aberrant expression of the enzyme was reported in many solid neoplasms. This study aimed to investigate the biological relevance of GSK-3ß in classical Hodgkin lymphomas (cHL). METHODS AND RESULTS: We analysed the functional status of GSK-3ß enzyme in cHL by using antibodies raised against fixation-resistant epitopes of phospho Y216 GSK-3ß (active form), phospho S9 GSK-3ß (inactive form) and ß-catenin protein. We first detected the pY216 GSK-3ß active form of the enzyme in 100 of 100 (100%) of the cases, and in line with the latter expression profile, the ß-catenin protein was found in only 12 of 100 (12%) of the samples. As reported previously in bladder cancer, pancreatic adenocarcinoma and chronic lymphocytic leukaemia, we showed an aberrant nuclear localization in the neoplastic clone of active pY216 GSK-3ß in 78 of 100 (78%) of cHL cases. CONCLUSIONS: We demonstrated the activation of GSK-3ß in cHL resulting in inhibition of the Wnt/ß-catenin signal cascade and the aberrant accumulation of its activated form in nuclei of Hodgkin Reed-Sternberg and Hodgkin cells. These findings may be relevant for future clinical studies, identifying GSK-3ß as a potential therapeutic target for cHL.

A targeted mutational landscape of angioimmunoblastic T-cell lymphoma.

The genetics of angioimmunoblastic T-cell lymphoma (AITL) are very poorly understood. We defined the mutational landscape of AITL across 219 genes in 85 cases from the United States and Europe. We identified ≥2 mutations in 34 genes, nearly all of which were not previously implicated in AITL. These included loss-of-function mutations in TP53 (n = 4), ETV6 (n = 3), CCND3 (n = 2), and EP300 (n = 5), as well as gain-of-function mutations in JAK2 (n = 2) and STAT3 (n = 4). TET2 was mutated in 65 (76%) AITLs, including 43 that harbored 2 or 3 TET2 mutations. DNMT3A mutations occurred in 28 (33%) AITLs; 100% of these also harbored TET2 mutations (P < .0001). Seventeen AITLs harbored IDH2 R172 substitutions, including 15 with TET2 mutations. In summary, AITL is characterized by high frequencies of overlapping mutations in epigenetic modifiers and targetable mutations in a subset of cases.